U.S. Pat. No. 4,054,931 (Bolton et al.) discloses a magnetic recording disk file consisting of a sealed housing in which one or more rigid magnetic recording disks are rotated at high speed. Recording heads, arranged adjacent to each recording face of the disks, initially rest on the disk surface but float upon a thin film of air when the disks rotate at operating speed. Because particulate matter trapped between the heads and the disks would damage the recording surfaces, the air within the housing must be exceedingly clean. In order to keep the air clean, an air impeller mounted on the free end of the disk spindle draws air downwardly through a main filter near the top of a housing. The filtered air flows outwardly and then upwardly to recirculate through the main filter. The rotation of the disks also forces air outwardly, thus supplementing the air flow to carry to the main filter particulate matter generated when the heads contact the rotating disks.
In the disk file of U.S. Pat. No. 4,147,299 (Freeman), recirculating air is channeled through an absolute filter, past a head-disk assembly and to an air-diverter valve which is thermostatically controlled to exhaust as much of the air as is necessary to maintain the temperature within a desired range. The recirculated portion of the air is returned to an intake plenum which also receives make-up air through an intake filter to replace the exhausted air.
The air-flow system of U.S. Pat. No. 4,147,299 should provide a far cleaner environment than does the system of U.S. Pat. No. 4,054,931, especially when operated with the air-diverter valve closed.